Hydrated lime product and method of making the same



Patented July 1, 1947 umi'rs p STATES PATENT OFFICE HYDRATED'LIME PRODUCT AND 'METHOD OF MAKING THE 'SAME Leonard John Minnick, Gheltenham,Pa., a ssignor to G. & W. H. Corson, I nc.-,-Plymouth lVIeeting, Pa., acorporation of Delaware No Drawing. ApplicationJul-y 2,1943, Serial No.493,288

4 Claims. 1

The present invention relates to aprocess for the treatment of dryhydrated lime and to the resulting product. The invention is directedtothe treatment of a dry lime hydrate which normally possesses theproperty, when mixed with water, of retaining its initial softconsistencyupon soaking, to impart thereto theproperty of forming astiff :mass with water which becomes softer when -worked,-making theproduct especially valuable for use as-a finishing lime and for otherpurposes.

This application is a continuation-in-part of my 'copending application,Serial No. 422,593, filed December 11, 1941.

At the-present time, several types of lime are available to the trade,for example, lump lime, pebble lime, pulverized quicklime, allrepresentint, types of unslaked quicklime that can be .prepared on-thejob. This material-must=be=slaked to a putty and should be soaked for atleast twenty-four hours, and when used for finishing purposes, should bescreened to remove any foreign matterthat may bepresent. Another type oflime that is commonly used is hydrated lime, in the form of a dry powderwhich has been prepared by slakin the limeinsome =form of 'hydrator atthe time of its manufacture. When supplied to the -job,:it is customaryfor this material to -be'soaked with water and a period of several hoursat least, and of twenty-four hours in general, of soaking is therecommended practice.

The above-mentioned limes, when prepared-for use, will change inconsistencytoa stiff mass-upon aging; When this putty is then workedwith a trowel, I a considerable amount of this stiffness is broken downand a soft workable consistency results. Thus-it is-oustomary whensoaking abox of lime-to add-tothe water asufficient quantity of the limeproduct to form a soft sloppy mass. On standing "overnight, this masswill stiffen to a pointwhere the putty will-become-rigid or'gelled, andin effect will resemble the consistency --of creamcheese. -In'this-form, the material can be conveniently handled inahod and-can'betransported from'the box to the point where it is :to be used. Themechanics'of this stiffening action is not clearly understood.In-thecaseof'dolomitic lime, the gelmay be infiuenced by the hydrationof anymagnesiumoxidethat is'present. In the case of high calcium limes,however, wherethere isno material that is available for reaction withthe watergthe mechanism is :rather =obscure. 4 In general, this propertymay be compared with. the thixotropic nature of various colloids,, whichwill 2 forma-gelwhen mixed with water, -becom ing fluid when agitated,andreturning to a stiff gel when, allowed-to stand. in the case of mostlime putties, however, once the mass has been worked, it- ,willrestiffen only at a very slow-rate.

In the case of most hydrates, the length oftime for which the hydratesmust be soaked to form the stiff mass depends upon the particularhydrate 'employed, but, as will hereinafter appear, certain speciallyprepared-hydrates do not form the stifi mass described, possessing theproperty of substantially retainin their initial soft consistency uponaging with water. =In the ease of the specially prepared hydrates whichpossess the property of substantially retaining their initialsoftconsistency upon aging with water, the -treatment-impar-ts tothesehydratestheproperty of forming astiff mass withwatersimilar to thestiff mass obtained with the hydrates of the usual types. 7 V

Among the dry hydrated lime products which possess the property ofretaining their initial consistency upon-aging-with water are theproducts hydrated by themethods described in-Patout No. 2,309,168,issuedJanuary-26,1943, andin copending application filed in the-name of'Bolton L. Oorson, Serial No. 345,498, filed-July {15/1940 (now PatentNo. 2,409,546), The hydrates .preparedin accordance with-thesemethods,in which the lime is dehydrated at super-atmospheric steam pressure alsohave,in general, the-novel characteristics of forming a-lime putty ofmaximum properties substantially immediately after mixing the dry powderwith water. Thus,-lime which has been hydrated by the methodsmentioned-attainsits maximum or ultimate plasticity, sand-carryincapacity, and general workability substantially immediately upon mixture"with water. Furthermore,the-consistency of theputty that is formed whenthe dry powder and water are mixed together reaches-substantially itsultimate value at onceami when this fluid material is permitted to'standfor -a period- 01 hours, there is noappreciable-change inthe'consistency of the putty. This featureis of tremendous value whenthe lime is mixed with sand as a mortar for masonry work. For instance,it obviates the necessity of retempering the mortar on. the mortarboard, and this, of course, sayes an appreciable-amount-of time duringapplication. v

lt may-also-bepointedout that while the product made by the methodsdescribedin 7 the abovementioned patent :and application possessespropertiesnot heretofore -availablein a dryllime hydrate and is beingwidely used in cdnnection 3 with lime in masonry, stuccoes, etc., theuse of this product will be further advanced in the field of finishinglime if a stiff putty which can be handled in a hod can be made from italmost immediately. When the above product is further processed inaccordance with the process of this application, this additionalproperty is developed, 7

and thus full advantage may be taken of the unusual qualities of theabove product. That is to say, this product may have water added to itand a perfect stiff putty formed almost immediately, and this stifiputty handled the same as the stiff putties which were formed after manyhours of soaking by other limes, the net result being that such aproduct may not only be handled and applied more quickly with theobvious saving in time and space required, but also all of the virtuesare present in the lime itself, such as high plasticity, sand-carryingcapacity, strength, adhesion, and soundness. The present invention asstated is applicable for the treatment of such hydrates to impartthereto the property of forming a stiff mass upon mixing with water,which mass becomes softer when worked.

One of the objects of the present invention is to provide a process forthe manufacture of a dry hydrated lime which normally possesses theproperty of retaining its initial soft consistency upon aging with waterto impart thereto the property of forming a stiff mass that becomesappreciably softer when worked, and, hence, of improved suitability forapplication.

A further object of the invention is to furnish a process by which a drylime hydrate of the type described, capable of forming with water, dueto its unusual aifinity therefor, a homogeneous mass devoid of any dryor agglomerated material, may be easily and economically prepared.

Still another object of the present invention is to provide a method forthe production of a dry lime hydrate of the type described whichpossesses improved plasticity as compared to the untreated hydrate.

A more specific object of the invention is to provide a process forimparting the aforesaid properties to a lime hydrate which attains itsmaximum properties substantially immediately upon mixing with water. 7

Other objects, including the provision of a dry hydrated lime producthaving the properties herein set forth, will be apparent from aconsideration of thespecification and claims.

In accordance with the present invention, dry, finely divided limehydrate of thetype described is mixed with a carbonate-supplyingingredient which provides the hydrated lime product with a coating ofcalcium carbonate of thioxotropic type when the product is mixed withwater. This calcium carbonate associated with the hydrated limeparticles imparts to the hydrated lime the property of forming a stiffmass upon mixing with water, which mass becomes softer when worked. Aswill hereinafter appear, the carbonate-supplying ingredient may becarbon dioxide adsorbed on the particles of the dry lime hydrate or byan adsorbent, or made available by chemicalreaction when the hydratedlime product is mixed with water, or it may be a carbonate which issufiiciently soluble in water to furnish carbonate ions forreaction-with the hydrated lime.

' Obviously, the carbonate may be supplied by more tha one of theaforesaid sources.

-When the dry, treated hydrated lime product is mixed with water, thecarbonate-supplying ingredient provides carbonate ions in solution, aswill be further discussed, and these ions react with calcium ionsresulting from the solution of calcium hydroxide in the water to formcalcium carbonate on the hydrated lime particles. It has been found thatthe calcium carbonate thus formed is of a particular type which producesthe desired result. It is believed that the desired stiffening orgelling effect is produced as the result of the ability of the calciumcarbonate to hold adjacent water in a temporary bound or oriented state,and the particular type of calcium carbonate formed is, therefore,designated herein as thixotropic-type calcium carbonate. This propertyis typical of that found in thixotropic suspensions, such as ferroushydroxide in water, although, in the case of the calcium carbonateformed when the product of the invention is mixed With water, the masswill not readily stiffen after being worked. This calcium carbonate musttake up its associated bound Water in a relatively quiescent state afterthe lime solid has been mixed with the water. Once the stiffened mass isdisturbed, such as by working with a trowel, the'bound or oriented wateris released and a softer working mass results. If any residual unreactedcarbonate-supplying ingredient remains which has not reacted with thecalcium hydroxide of the lime, then upon further standing of the mass,which has been worked, a further stiffening effect will result, thedegree of which will be dependent upon the amount of unreacted reagentand the time allowed for the reaction to proceed.

As pointed out, the carbonate-containing ingredient mixed with the dryhydrated lime provides the hydrated lime particles, when the product ismixed with water, with a coating of thixotropic type calcium carbonate.In the case carbon dioxide is the carbonate-supplying ingredient, thecarbon dioxide derived from any of the aforementioned sources dissolvesin the water when the dry hydrated lime product is mixed therewith.forming carbonic acid, and the carbonate ions thereof are then availablefor reaction with the hydrated lime. When a carbonate furnishingcarbonate ions is employed, the carbonate ions are formed when theproduct is mixed with water, and these ions then react with the hydratedlime to form the thixotropic-type calcium carbonate. A small portion ofthe carbonate-supplying material may react with the particles of limehydrate in the dry state, for instance, when the dry hydrate contains asmall amount of free water, but in any case, unreactedcarbonate-supplying material will be available for reaction to form athixotropic-type of calcium carbonate when the product is mixed withwater.

As previously stated, a dry hydrate of the type prepared by hydratingunder super-atmospheric steam pressure and which possesses the propertyof retaining its soft consistency with water, and which attains itsmaximum properties substantially immediately after being mixed withwater, is treated in accordance with the present invention. Theprocesses described in the aforesaid patents produce such a hydrate,and, hence, may advantageously be employed in the preparation thereof.

As previously stated, the lime hydrate treated is dry, that is, it hasthe properties of a powder. When a carbonate is used as thecarbonate-supplying material, the moisture content of the dry hydratedlime is relatively immaterial and the c tes-see;

i usual hydrated limecontaining ab'outi3 or more off-ree water' may beemployed;- The -term' dry. lime hydrate asusedi herein; unless otherwisequalified, inc1udes=hydrates-that have" theprop erty 'ot a powder;although: as" pointed out they" may contain somei-ree water;

When carbon dioxi-deservesas the carbonate-.- supplyingingredienttheuseofsubstantially bone dry" hydrated lime is preferred; since:' the most":marked-' results-are thenobtained: However;ldry. hydrated limecontaining: a small amount: of free water; fo .example; up to about: 1maybeused; although such approduct may; tend. 130s lose. some of itsadvantageous 1 properties on: storage. Asa general" rule, the lower-.-the water content, thebetter; and unless asubstantially bone dryhydrated lime is: employed, the use. of a .dry. hydratedlime-containingnot more than 0.2%.to 0.4%" free'wateris preferred.

Referring t the carbonate-supplying; material, the-use-of carbondioxide. adsorbed on-the particlesof the drylimehydrateis the nowpreferred material. As stated, however,.carbon dioxide may be furnishedby mixing, with thedry hydrated lime, amaterial. such as silica gel orActivated Alumina in which carbon. dioxide gas is adsorbed; or.-amaterial containing a carbonate (usuallya mixture of .two: ingredients)which reacts upon contact with water to release carbon dioxide atca,rate faster thanthe carbonate can reactiwiththellimevdue to ioninterchange. In this; case, the released gas, dissolves in the water,formingcarbonic acid as previously explained. Itiwillthus bev seen thatthis material actsin substantially thesameway as carbon dioxide ad--sorhedzonx. the; particles or: the: dr lime; hydrate, or. by anadsorbent, and, hence, these means of supplying the carbonate areincluded herein withim the: phrase carbon,dipxide-supplying in?gredient. When the dry hydrated lime is treated. with a carbondioxide-supplying ingredient, the rate.v of stiffening of the resultinglime product; when treated with water, israpid, and the time requiredfor soaking can be reduced to a very short time, if desired, even to afew minutes.

The carbonate-supplying,materialmay be any inorganic carbonate ofgreater water-solubility thancalcium carbonate, thus furnishingcarbonateions in the presence of water. Examples, of carbonates that areapplicable for use are so.-- dium or potassium. carbonate orbicarbonate, magnesium carbonate, Zinc carbonate, ammoniumcarbonateorbicarbonate, and lead carbonate. Lead carbonate, however; forms acolored reaction; product with thehydrated lime and carbonates. of this.type are enerall not. pr r In cases; where thepresence of' a.relativelysoluble reaction product between the lime hydrate and the carbonate(such asis formed when a. sodium or potassium carbonate is employed) isobjectionable, the use oi'a compound which forms relatively,- insoluble.reaction, products, for. BX; ample;,magnesiumor-zinc carbonate isrecom,- mended. Of the carbonates available for use,precipitatedmagnesium carbonate ispreferred. The various carbonates donot'develop the maximum properties in thesame length of time, and, ingeneral, the more soluble the carbonate, the more rapid is the reaction.For example, the use of sodium or-potassium carbonate gives a relativelyrapid stiffening effect as compared .tothe use of an equal quantityofmagnesium or zinc carbonate,- Ingeneral;- a hydrated: lime with whl'ch-a carbonate ot the typediscussed is-mixedi stiiiensaat a-- materially-slowerrate than;- isthe case when the; lime is associatedi withararb'on dioxide-supplying:material; In; the case of: the: use of 'arelatively insoluble-carbonate-,-. th,e:ti1, ne;

required forlsoaking, may: extend overxaperiodi f.

an hour or more. The rateof stiffeningmay be, observed whena. carbonateforming; a:. colored tively. small, namely, a few; tenths per cent:.,forinstance, 0.2 130.05% on, the basis of the-hydrate. Therefore,- theamountof carbonate-sup,-

plying: material; required. may; alsobe relatively In the case carbondioxide adsorbed; on,

small. the particles of the. dry: hydrated lime serves;v as

the carbonate-supplying gmaterial; theamount. of;

CAhbOlCltdiOXldE which: can be adsorbed; is,-limi-ted-, andinmost'instancesan adsorption ofabout. 1%. carbon. dioxide will; befound tobe the maxi:

mum. The use ofv adsorbedz'carbon.- dioxide in. amounts aslow as 0.1%have been foundtobesatisfactory and. the preferable 1 range, is; from0.2% to 0.5% adsorbedcarbon. dioxide. Inthe case that the carbonatelSSUDDIiGd'ZfIOmTChB: other sources, thea'rnount employed may'alsobe-rela-- tively small, for example, with relatively soluble;

carbonates, an amount of carbonate correspond: ingtothe small amountofzthixotropic-type:cal:

cium carbonatetobeiormedimay'be used; In the; caseof a relativelyinsoluble carbonate, the: amount may be increased" so thatthe desired,=stiffening action will beobtained-in the desired:

time, for instance, twice or three timesxthatrequired to give the amountof: thixotropic-type; calcium carbonate required may-bezused; The: upperlimit of carbonate-supplying niaterialis.

relatively immaterial, since usuallyan excess will not interferewiththe-productorthe properties thereof, but, in. general, the useofimore than about3% to 5% oi the material ,willrnotabe em.- ployed,although, for example, in'the caseofxmagnesium carbonate, the use of asmuch as"l0 and higher-has been 'fOlllldZtO perform very well: andwithout deleteriously affecting the other charac teristics of theproduct when added to. the hydrated limes which possess the property ofsub.

stantially retainingtheir initial soft consistency. upon-aging withwater such as thev products prepared aby-lthe' methods described in theaforesaid" patent and application. Of: course, in: the case:

of a highly soluble carbonate, the use-of:- a large;

excess is not desirable, since the products-oileaction may interferewiththe other characteristics of the product when it is employed'for build.-ing and construction purposes. The useof a large excess over thatrequired isnot recommended in.

any case, since it represents an economic loss, the excess material orthe reaction products: thereof merely serving as adulterants orfillersin the product; v

V In preparing the product of the invention, ex. cept' when carbon.dioxide-adsorbed by. the particles I ofthe lime-hydrateis, thecarbonate-supply! ing material; the carb'onate-supplying material maybemixed with the dry, finely: dividedzhyz. drated liine in any desiredmannen-which..pro vides atuniformmixture ottthe' lime particles and thecarbonateesupplying: material, Advantageouslyy the carbonateesupplyingmaterial, as well as -the:-

hydrated: isms,- is: in. fii'iel-ya. divided. form;-WITie'mthe-processessofzPatentgNm 2,;3fi9ih58' 7 and of Patent No.2,409,546 areemployed, the carbonate-containing material may,'f0rexample, be mixed with the hydrated. lime after'discharge of thehydrated'product from the pressure hydrator, in which it has beensubjected to superatmospheric steam pressure and priorto the treatmentof thehydrated lime in the tube mill, the action of the tube mill beingrelied upon to mix intimately the two components of the product. Themixing of the dry hydrated lime with the carbonate-containing materialmay be carried out at any convenient temperature, but in the case anadsorbent holding the carbon dioxide is to be mixed with the dryhydrated lime, the mixing will take place at a temperature below thatwhich will drive the carbon dioxide from the adsorbent--the lower thetemperature, the better.

In the preparation of the product where carbon dioxide adsorbed by theparticles of lime hydrate is the carbonate-supplying material, thecarbon dioxide may be furnished from any suitable source, for example,from carbon dioxide gas under pressure, from dry ice, or from flue. gas,kiln gas, etc. The process may be conducted at atmospheric pressure, atan elevated pressure, or under a vacuum. The adsorption, for example,may be brought about in an open chamber with the carbon dioxide, eitherpure or diluted with another gas, such as air, passing over the surfaceof the powder, the powder being in a relatively thin layer or in largerbulk, in which case it may be turned by a suitable arrangement of mixingblades to bring it into contact with the carbon dioxide, or the drypowder may be dropped through an atmosphere of carbon dioxide gas; andthe process may be conducted either in a continuous manner or batchwise.In one method, a known quantity of the dry hydrate is placed in a closedchamber provided with a mixing mechanism, and carbon dioxide is passedinto the chamber, building up a small pressure therein The mixingmechanism is then turned on and operated until the dry hydrated lime hasadsorbed the carbon dioxide from the chamber and the pressure has beenreduced to a constant value. The reduction of pressure to a constantvalue is a gauge by which it is possible to determine when the desiredadsorption has been obtained. If desired, the closed chamber may beevacuated to a suitable pressure lower than atmospheric, and the processcarried out by pass ing carbon dioxide in the desired amount into thechamber to create a higher pressure, the process being completed whenthe pressure drops to a constant Value. If desired, the chamber may beevacuated to a very low positive pressure, for instance, in theneighborhood of to 10 microns, thus freeing the dry hydrated lime fromadsorbed air and moisture. The carbon dioxide may then be added in anamount corresponding to that to be adsorbed or in excess thereof. Thedry lime hydrate may, of course, be treated by other methods by whichthe carbon dioxide is adsorbed,

The treatment of the dry hydrated lime with the carbon dioxide may beconducted at any desired temperature at which adsorption will takeplace. Generally, the lower the temperature of treatment the moreefficient will be the adsorption and for this reason hydrated lime atroom temperaturewill usually be treated. However, lime at an elevated.temperature, for instance, lime immediately upon its removal from thehydrator at a temperature of 175 F. may be treated,

but generally, the lime will be treated at ateinperature below F. .'1hedesiredadsorption as previously indicated takes place rapidly and thereis no necessity for the application of external heat; in fact, this isto beavoidedsince it is merely a Waste of energy, and the amount of gasadsorbed is reduced. Carbon dioxide will not react with bone dry calciumhydrate, but-when moisture is present, there is a tendency forcarbonatation. Therefore, if the lime treated contains a small amount offree Water. some exothermic heat may be generated due to a carbonatationreaction. Since it is known that the carbonatation reaction, is favoredby elevated temperatures, it-is evident that a relatively lowtemperature should be sustained throughout the treatment whenthehydrated lime contains free moisture. Although Water isa'product ofthe carbonatation reaction, the amount produced is so small that it hasno deleterious effect. In the preferred case where moisture is absent,treatment of hydrated lime with carbon dioxide gas does not generate anyappreciable amountof heat.

As previously pointed 0111;, although there may be a small amount ofcarbonatation, carbon dioxide is nevertheless adsorbed by the particlesof the dry lime hydrate and it is the adsorbed carbon dioxide that isrelied upon to give the described properties to the lime product. Otherforms of carbonate may also be present in the dry hydrated lime product,for example, carbonate resulting from incomplete burning of the stone inthe lime kiln. In addition, carbonate may be formed when hydrated limeis stored for lOIlg periods of time in paper bags. These carbonates andthe addition of calcium carbonate solids to the hydrate do not have anyeffect on the stiffening action of the hydrate such as is obtained bythe present invention.

It has been found that, when a hydrate of the type described has beentreated in accordance with the present invention, the affinity which thedry powder has for water is greatly enhanced, and, therefore, by merelydumping the dry powder into the proper proportion of water and pushingthe material under the surface of the water with some convenientimplement, the powder absorbs the Water at an extremely rapid rate andafter a few minutes the entire mass is homogeneous and devoid of any dryor agglomer ated material. It has also been found that the material thustreated will require a larger amount of water than the untreatedmaterial, and that, in spite of this additional water, the resultantputty will stiffen into a rigid mass which, when worked, for examplewith a trowel, becomes appreciably softer and more suited, therefore,for application. Another benefit derived from this treatment isillustrated by the fact that the plasticity of the putty formed from ahydrate prepared in accordance with the method of Patent No. 2,309,168is as follows:

Plasticity of untreated hydrate measured immediately after mixture withwater 270 Plasticity of treated hydrate measured immediately aftermixture with water 310 The plasticity is measured on the Emleyplasticimeter, as developed and standardized by the United States Bureauof Standards.

Aging the soaked treated hydrate, preparedfrom a hydrate which attainssubstantially its maximum properties immediately upon mixing withwatenhas little effect on the plasticity of the putty and otnerproperties, although in some instances, the treated hydrate has shown asmall increase in plasticity when soaked overnight, but this increaseoffers little practical advantage. It is to be understood, however, thatif desired the above or any of the putties obtained from the treatedhydrates can be soaked and aged before use.

The rate at which the stifiening of the putty takes place can be furtheraltered by the use of retarders or accelerators. Thus, when the hydratedlime has been treated with a carbon dioxide-supplying material, a smallamount, for example a few tenths of one per cent., of cream of tartar,Rochelle salt, sugar, glycerine, or other similar retarders will slOWdown the rate of stiffening, and such materials as magnesium sulphate,aluminum sulphate, and other salts of this type will increase the set toa point where the material practically takes a flash set when mixed withWater. For practical purposes, the use of retarders and accelerators is,however, generally not necessary since the carbon dioxidetreatedmaterial will stiffen at a rate that is convenient for practicallyimmediate use of the Putty.

Theembodiment described herein in which an inorganic carbonate ofgreater water solubility than calcium carbonate is mixed with thehydrated lime, hereinabove defined, to impart thereto the property offorming a gel in admixture with water is not claimed herein but is thesubject-matter of my copending application Serial No. 713,465, filedDecember 2, 1946, as a division of the present application.

Considerable modification is possible in the methods of treatment of thedry hydrate of lime with the carbonate-supplying material, as well as inthe conditions employed during treatment, without departing from theessential features of the invention.

I claim:

1. The process of treating a dry finely divided hydrated lime which hasbeen hydrated under super-atmospheric steam pressure and which attainssubstantially its ultimate properties, including fluid consistency andplasticity, substantially immediately upon mixing with water, whichfluid consistency remains substantially the same upon aging with water,to convert said hydrate into a product in dry powdered form capable offorming a gel in admixture with water which gel upon subsequent workingreverts to fluid consistency and to impart other improved properties tosaid hydrated lime, including an increase in the afiinity of saidhydrate for water, which comprises mixing carbon dioxide with saidfinely divided hydrated lime containing less than about 1% of freemoisture in an amount between about 0.1% and about 1.0% by weight, basedon the weight of said hydrated lime, at least a substantial portion ofsaid carbon dioxide being non-reacted chemically with said dry hydratedlime to provide a product which when mixed with water formsthixotropic-type calcium carbonate on the particles of said hydratedlime and thus imparts said properties to the product.

2. The process of claim 1 wherein the dry finely divided hydrated limewith which the carbon dioxide is mixed contains less than about 0.4%free moisture; wherein the carbon dioxide is brought into contact withsaid finely divided hydrated lime and is adsorbed on the particlesthereof; and wherein the amount of carbon dioxide adsorbed is betweenabout 0.1% and about 0.5% based on the weight of the hydrated lime.

3. A dry finely divided hydrated lime of improved properties, includingan increase in the affinity of said hydrate for water, and characterizedby its ability to form a gel in admixture with water comprising amixture of dry finely divided hydrated lime which has been hydratedunder super-atmospheric steam pressure and which attains substantiallyits ultimate properties, including fluid consistency and plasticity,substantially immediately upon mixing with water, which fluidconsistency remains substantially the same upon aging with water, andcarbon dioxide mixed with said hydrated lime in an amount between about0.1% and about 1.0% by weight, based on the weight of said hydratedlime, at least a substantial portion of said carbon dioxide beingnon-reacted chemically with said dry hydrated lime to provide a productwhich, when the product is mixed with water, forms thixotropic-typecalcium carbonate on the particles of said hydrated lime to convert theproduct of fiuid consistency first formed into a gel in admixture withwater, which gel upon subsequent working reverts to fluid consistency.

4. The product of claim 3 wherein the carbon dioxide is adsorbed by theparticles of said hydrated lime and is between about 0.1% and about 0.5%and wherein the dry hydrated lime contains less than about 0.4% of freemoisture.

LEONARD JOHN MINNICK.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,604,575 Holmes et a1 Oct. 26,1926 1,604,576 Mathers et a1 Oct. 26, 1926 1,732,409 Loomis et a1. Oct.22, 1929 2,013,811 Smith Sept. 10, 1935

